Biological signals such as electrocardiographic waves and photoplethysmographic waves have characteristics that artifacts (noise) due to body motion or the like is easy to be superimposed thereon. Patent Document 1 discloses a biological signal measurement device that extracts and detects a pulsation component of a subject from a measured signal superimposed with noise components such as an artifact component.
The biological signal measurement device includes a light irradiator that irradiates a biological tissue of the subject with two light components having different wavelengths, a light receiver that receives the light components having the respective wavelengths, which have been emitted from the light irradiator and have transmitted through or have been reflected by the biological tissue, and converts the light components to electric signals (biological signals) in accordance with light reception intensities of the respective light components, a Hilbert transformation unit that performs Hilbert transformation on the electric signals so as to generate pieces of envelope data forming envelopes, and an oxygen saturation calculator that calculates an extinction ratio based on the generated pieces of envelope data and calculates blood oxygen saturation in the artery in the biological tissue based on the extinction ratio.
Further, the biological signal measurement device measures the blood oxygen saturation by detecting the envelopes of the electric signals (biological signals) by the Hilbert transformation unit and performing normalization processing on amplitudes thereof. In addition, the biological signal measurement device relatively attenuates components other than a frequency component (pulsation component) in accordance with pulsation of the artery of the subject so as to calculate a pulse rate.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2012-024320.
The biological signal measurement device as disclosed in Patent Document 1 can deal with unexpected artifacts. However, the biological signal measurement device cannot sufficiently remove artifacts for a biological signal with the artifacts superimposed thereon steadily, resulting in a risk that the pulse rate cannot be calculated accurately. Therefore, a technique capable of removing artifacts more effectively and obtaining biological information robustly against the artifacts has been desired.